Triceratops is a very famous plant-eating dinosaur,armed with a bony frill and large horns.It appears in the menu(on the PS3 version)walking around,then it stops to eat a few plants,then it walks away.
Through the game,only one Triceratops is seen,dead,next to a river,and aparently being eaten by a Deinonychus.A pack of Deinonychus could have killed it,or the raptor was just scavenging from the carcass when it came across it.